package bfsalgorithm;

import java.util.LinkedList;
import java.util.Queue;

/**
 * 200、岛屿数量
 */
public class Exercise2 {
    int[] dx = {0,0,1,-1};
    int[] dy = {1,-1,0,0};
    int m;
    int n;
    boolean[][] visit;

    public int numIslands(char[][] grid) {
        m = grid.length;
        n = grid[0].length;
        visit = new boolean[m][n];

        int ret = 0;
        for(int i = 0;i < m;i++) {
            for(int j = 0;j < n;j++) {
                if(grid[i][j] == '1' && !visit[i][j]) {
                    bfs(grid,i,j);
                    ret++;
                }
            }
        }

        return ret;
    }

    public void bfs(char[][] grid,int i,int j) {
        Queue<int[]> heap = new LinkedList<>();
        heap.add(new int[]{i,j});
        visit[i][j] = true;

        while(!heap.isEmpty()) {
            int[] t = heap.poll();
            int a = t[0],b = t[1];

            for(int k = 0;k < 4;k++) {
                int x = a + dx[k];
                int y = b + dy[k];
                if(x >= 0 && x < m && y >= 0 && y < n && grid[x][y] == '1' && !visit[x][y]) {
                    heap.add(new int[]{x,y});
                    visit[x][y] = true;
                }
            }
        }
    }
}
